Control of smooth muscle cell proliferation plays a critical role in several pathologic conditions including atherosclerosis, aneurysms, transplant vasculopathy, restenosis following endo-surgical stenting of vessels, and failure of vein grafts. Although excess vascular smooth muscle cell (VSMC) proliferation is involved in neointimal hyperplasia, and apoptosis of VSMCs is involved in aneurysm formation and atherosclerotic plaque rupture, much information has yet to be learned about how SMC proliferation is controlled in vivo and how said control fails in disease processes. This gap in knowledge impedes the development of new therapeutic or preventative measures aimed at correcting SMC dysfunction. This laboratory has recently discovered that interleukin-2 (IL-2) contributes to the maintenance of VSMCs in vivo. The overall goal of this laboratory is to understand the regulation and function of IL-2, and how impairment of either contributes to human pathology. The object of this proposal is to begin to establish the impact of IL-2 on VSMC biology. The central hypothesis is that IL-2 promotes the survival and maintenance of a differentiated phenotype in vascular smooth muscle cells. This hypothesis will be tested by the following specific aims: Aim I: Establish how monomeric and multimeric IL-2 influence VSMC function. This aim will be accomplished through testing the influence of IL-2 on several standard assays of VSMC function. Aim II: Determine whether VSMC release heparan sulfate- bound IL-2 and whether the released IL-2 influences VSMC function. This aim will be achieved through the use of a transwell assay, in which VSMC are separated from pieces of artery. Release of IL-2 will be assessed and heparanase inhibitors will be used to determine the role of this enzyme. Aim III: Establish the influence of IL-2 on aneurysm formation in vivo. This aim will be accomplished by Western blot analysis of the forms of IL- 2 present in human aneurysm tissue specimens, and by determining whether IL-2 can reverse aneurysm formation in IL-2 deficient mice. The proposed work is innovative, because it capitalizes on the novel findings that IL-2 is associated with heparan sulfate oligosaccharides present within large and small arteries and that in these location heparan sulfate-bound IL-2 influences VSMC phenotypes and survival. Completion of the proposed studies will provide an enhanced understanding of how vascular cell homeostasis is regulated via a here-to-for unknown pathway initiated by IL-2. This contribution is significant because the regulation of vascular cell homeostasis underlies a multitude of vascular pathologies, yet therapeutic interventions targeting smooth muscle cells are extremely limited. Since cardiovascular disease is the number one cause of mortality in the United States, this work addresses the NIH's mission to treat human disease. Knowledge gained from both proposed and future studies will support the establishment of new therapeutics, drug delivery systems, and even tissue constructs that target or utilizes smooth muscle cells. PUBLIC HEALTH RELEVANCE: Abnormalities in vascular smooth muscle cells underlie many pathologic conditions including atherosclerosis, aneurysms, and failure of vein grafts and transplanted organs. The proposed studies concern gaining a better understanding of how proliferation and death is regulated in vascular smooth muscle cells in both normal and disease states. The proposed research is of great significance to public health, given the prevalence of cardiovascular disease in the United States.